1. Field of the Invention
The present invention concerns an altitude and vertical speed indicator for aircraft.
2. Description of the Prior Art
For a rotary or fixed wing aircraft climbing or descending to a given altitude, for example a flight level required by air traffic control, is generally effected at a stable vertical speed.
On approaching the required altitude, the pilot of the aircraft progressively reduces the vertical speed of the aircraft so as to reach said altitude with a vertical speed that is sufficiently low to avoid any significant overshoot of the required altitude.
This reduction in the vertical speed on approaching the required altitude may be based on the pilot""s judgement or on empirical rules, the pilot monitoring the evolution (position and speed) of the altitude indication [a pointer on conventional instruments or an index in a system of symbols known in aviation as EFIS (Electronic Flight Instruments System)].
For example, one conventional empirical rule is to begin reducing the vertical speed on reaching a fraction of the distance between the required altitude and the current altitude ({fraction (1/10)}, for example), and to repeat this process to reduce the vertical speed progressively.
Nevertheless, regardless of the strategy employed (based on judgement or on the use of an empirical rule), these methods require a good knowledge and experience of the performance of the aircraft and introduce a significant workload into a change of flight situation, i.e. at a time when the pilot should be concentrating on other related tasks, for example air traffic or navigation. The following points in particular should be emphasized:
the method based on judgement requires continued attention to the altitude indicator. The anticipation altitude difference, i.e. the altitude difference from which the pilot must begin to reduce the vertical speed of the aircraft, is not necessarily easy to estimate, and the convergence with the required altitude must be monitored attentively if the procedure is not to be terminated too high or too low, which would make it necessary to resume the procedure for xe2x80x9cinterceptionxe2x80x9d of the required altitude, making it take longer;
using an empirical method, as described previously, the method is itself difficult to use since it is based on correlating two independent indications (vertical speed and altitude). It may also be complex if the interception altitude is not a round figure, for example, 1 875 feet), which is routine in approach procedures;
the pilot""s attention is concentrated on the two indicators throughout the anticipation maneuver, and then during adjustments to stabilize the required altitude, which has the following effects:
with conventional circular indicators, the task is difficult because of the need for a relatively wide visual scan between the two indicators, usually in the vertical direction (which is less xe2x80x9cnaturalxe2x80x9d than a scan in the horizontal direction) and the total absence of visual correlation, and therefore analogy, between the two indications (the movement and the dynamics of the pointers of the two indicators are different);
if the altitude indication is numerical or xe2x80x9cpseudo-numericalxe2x80x9d (multidigit drum for current value, plus scrolling scale) on a pilot display screen of an EFIS instrumentation, the difficulty of monitoring the vertical speed from the movement of the altitude scale and, more generally, the absence of specific visual aids for determining the anticipation altitude difference, despite the proximity of the two indicators, constitutes a heavy workload.
Document U.S. Pat. No. 4,860,007 discloses an altitude and vertical speed indicator for aircraft comprising:
first and second sensors for the altitude and the vertical speed of the aircraft, respectively,
means for processing the signals supplied by said first and second sensors, and
means for displaying the processed signals, having on a display screen:
altitude indication means, and
vertical speed indication means of an appropriate kind in line with said altitude indication means,
said altitude indication means and said vertical speed indication means being coupled so that the altitude indication in line with the vertical speed indication represents, at all times, a future altitude for the current vertical speed.
However, in the disclosure of this document, it is essentially a question of pointing to a chosen altitude value identified by a marker, by matching to the chosen altitude the vertical speed appropriate to this objective. Despite the presence of a marker of this kind, reading off the altitude from the position of the vertical speed pointer may remain doubtful for the pilot.
One aim of the present invention is to remove this drawback.
To this end, in the altitude and vertical speed indicator for aircraft of the invention, said altitude indicator means comprise a graduated scale vertically mobile past a fixed marker and said vertical speed indicator means comprise a pointer rotatable about the point of intersection of a straight line segment through said fixed marker and a straight line segment through said pointer and pointing towards said mobile scale, the angle defined by said fixed marker and said pointer being representative of the vertical speed value.
Accordingly, when the vertical speed indication lines up with the required altitude indication, all that is required is to maintain the vertical speed indication locked onto the required altitude indication until the latter is reached, which is reflected in a progressive reduction in the vertical speed to an at least substantially zero vertical speed. In particular, the presentation of the pointer in line with the vertically scrolling scale provides at all times a very close link between the altitude and vertical speed scales, by associating the future altitude with a vertical speed. Thus the indicator of the present invention provides the pilot of the aircraft with an analogous and interconnected indication, on a display screen, of altitude and vertical speed for guiding acquisition of a required barometric (or radar) altitude without displaying the current value of the altitude of the aircraft, until the required altitude is actually reached.
In particular, said pointer may be symbolized on said display screen by a straight line segment.
The processor means may include a digital computer for converting physical altitude and vertical speed data into data suitable for display on said display screen and a symbol generator for showing on said screen, based on information supplied by said computer, the graphical characteristics of the presentation of the altitude and vertical speed information, and, between said first and second sensors and said digital computer, a primary reference system supplying the altitude and vertical speed information in digital form.
The vertical speed indicator pointer is advantageously disposed between said artificial horizon and the altimeter on an aircraft instrument panel screen showing an artificial horizon.
The figures in the accompanying drawings indicate how the invention may be put into effect. In the figures, the same reference numbers identify similar components.